Short Prints and Squished Layers On Chitu-powered Resin Printers: Solution

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Many users of Chitu-powered resin printers complain that when they print flat on the bed, their prints are shorter than they should be – usually around 0.3–1 mm. This forces the users to print on supports. Back in the days when I started with resin printers, I observed the same thing on my Elegoo Mars. The cause of that was poor construction (see full explanation). I haven’t observed such problems on Elegoo Saturn ­– until now. Let’s explore what causes it and how to fix it.

You see people fighting this problem by leveling against a paper folded various number of times, setting arbitrary numbers to Z-offset and similar. Everyone has a custom recipe. I will give you my recipe which I think works the best – and unlike the others, I will explain you why. I tested everything on Elegoo Saturn, but I believe it applies to all Chitu-based printers.

Possible causes

There are two possible causes for the problem you observe – one is hardware, and the second one is software.

I own Saturn from the first and second pre-order batches. These Saturn have a counter bearing on top of the Z-axis to prevent the screw from moving. It is not the best solution, but it is better than nothing. From the photos that my readers sent me, it seems that newer Saturns don’t have this bearing. Unless Elegoo changed the motor’s construction, new Saturns might face the same problem as Mars (related blog post). However, I doubt that Elegoo would make the same mistake, so I don’t believe this is the root cause. However, since I don’t own new enough Saturn, I cannot confirm this.

The second cause is purely software one: I started experiencing shorter prints after updating Saturn’s firmware to V4.4.3. When I observed the printer during operation, I noticed how much does the printer’s construction bend. I also noticed that the movement of the printer is strange – during the printing of the bottom layers, the printer actually moved pass the limit switch. When I measured it, the printer moved 0.5 mm below the limit switch. This wasn’t the case before.

Therefore, you level your build plate when the Z-axis is on the bottom switch and then, when you print, it moves lower. This is the source of squished layers. I think there is a hard-coded constant in these printers that tells the printer to start printing below the home position. We might only speculate why is this “feature” here. But I see two possible explanations:

  • it is a measure to build up a large force to speed up resing squeezing during the formation of the bottom layers. The goal is to probably fight insufficient bed adhesion. There are better ways to get the adhesion just right: read my posts on this topic: Introduction and a practical guide.
  • alternatively, this might have something to do with leveling cards that people were asking for. These cards make no sense, but people asked for them (oh no, you cannot level agains bare LCD! You will damage it. No, you won’t). And it is a way to counteact their thickness.

It is sad that the behavior is undocumented and it only makes me distrust Chitu closed ecosystem even more. Nevertheless, there’s a simple solution.

How to level your build plate to avoid squishing layers

Since we know the printer moves below the home switch, we know that we can’t level the build plate when the printer is in the home position. Instead, we want to level the build plate when it is on the starting position of the print. Therefore:

  • create a dummy printer file – e.g., with a small simple model. Setup layer thickness 0.01 mm (the smallest Chitu slicer allows you to). Slice the file and prepare it for printing. I don’t provide this file as you have to slice it for the machine you have.
  • Prepare your printer such that there is an empty and clean tank in place.
  • Loosen screws on the build plate.
  • Mount the build plate on the printer.
  • Start printing your dummy model.
  • Once printer starts exposing the bottom layer, turn the printer off. In this way, the build plate stays in the position where the printer truly starts the print.
  • Tighten the screws.

That’s it. Now you have properly levelled your printer such that there are no squished layers. Give it a try and let me know in the comments. Note that you should also add sufficient rest times to your bottom layers to get the build plate adhesion just right and remove elephant foot: Introduction and a practical guide.

And what about the paper? And how do I ensure my build plate is flat?

Surprisingly, people are very opinionated about the way you level. One common way you hear is that you have to use the traditional machinist way of using a paper or thin metal sheet moving under the object and finding out when it grips.

This is indeed a very common and traditional method of finding Z-offset e.g., on a mill. It is used as you don’t want to scratch the surface via the tool. However, we don’t have such a problem with the build plate. Also, you don’t have a way to offset the sheet thickness.

The second argument you hear “But how do you make sure that the build plate is flat and all corners sit on the LCD?”. Well, easy – just push it slightly or rely only on the spring in the build plate. It is enough as there are no forces to counteract. Also, if you are scared that the screw will grip the ball of the build plate, don’t be. There is an aluminum sleeve/collect to grab the build plate’s ball, so the screw never grips the ball. Also, it is possible that the build plate is not straight and not all corners are laying on the LCD. You will detect this with a thin sheet, but what can you do about it? If it is not flat, there is no way to level it so all corners sit flat.

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